The present invention relates to a method and apparatus for adhering a work piece to a support member for subsequent use in a machine tool or the like, and more particularly to a method and apparatus for aligning and mounting an optical lens precursor, e.g., a contact lens button or blank, on a pitch block for subsequent insertion in a lathe to fabricate an optical lens.
In one method for the manufacture of optical lenses, a substantially cylindrical lens precursor is inserted in a lathe. A curve, for example, a concave or base curve, is cut into one of the end surfaces of the precursor with a cutting tool. The position of the precursor in the lathe is then reversed, and a power curve is cut in the opposing surface of the precursor to produce an optically efficient lens. A method and apparatus for performing such cutting operations, along with a preferred lens structure, are disclosed in more detail in commonly assigned U.S. application Ser. No. 928,978 filed July 28, 1978, the disclosure of which is hereby incorporated by reference thereto.
During the cutting operation, the lens precursor should not be compressed or otherwise have any forces exerted thereon, to thereby avoid having the precursor assume a shape other than that which it naturally assumes in the absence of these forces. For example, if the precursor is made from a resilient material, such as a hydrophilic polymer used for soft contact lenses, and the precursor is supported in the lathe by means of a chuck or the like which applies a radial compression force thereto, the curve which is cut into the surface of the precursor may become distorted when the precursor is removed from the chuck and resumes its natural shape. This problem becomes particularly acute in the manufacture of contact lenses and other optical elements requiring very precise tolerances. Any slight distortion of the curve upon removing it from the chuck may take it out of the tolerance range of the particular prescription for which it is designed, thereby rendering it useless for its desired purpose and resulting in substantial waste.
Therefore, it is necessary to support the lens precursor in the lathe in a manner which will not exert any distorting forces on the precursor. This function is generally accomplished by adhering a support block, commonly referred to as a "pitch block," to the surface of the precursor opposite the surface on which the curve is to be cut. The pitch block can then be inserted into a chuck on the lathe and clamped thereby to support the precursor in the lathe without exerting any distorting forces thereon.
In the past, the mounting of a lens precursor on a pitch block has generally been carried out in a manual operation. An operator would dip one end of the pitch block into a pool of liquid adhesive, or pitch. The pitch block would then be placed on a rotating support, such as a potter's wheel, with the adhesive end up. The operator would manually center the block on the wheel. Once the pitch block is centered to the best of the operator's capability, the lens precursor is then placed on the adhesive end of the pitch block and centered thereon, using only the operator's hands and eyes as alignment guides.
This manual operation for mounting a lens precursor on a pitch block possesses numerous disadvantages, the foremost of which is the limited accuracy of alignment which can be obtained. In the manufacture of optical lenses, and in particular for contact lenses, it is essential that the two surfaces cut on opposite sides of the precursor be concentric. If they are not, the desired optical correction cannot be obtained with the resulting lens. Using only their eyes as a guide, even the most skilled operators are only able to obtain concentricity within 0.004 to 0.005 inch. As lenses become smaller and thinner, this tolerance range may not be adequate to achieve the desired optical effects. Furthermore, the human factor present in the precursor mounting operation substantially reduces the controlled repeatability which can be obtained in such an operation.
In addition to the alignment accuracy and repeatability problems, another problem attendant with the prior art mounting operation is the amount of time which is consumed for each operation. In view of the fact that the operator is required to visually align and check each precursor as it is mounted, each mounting operation will consume a substantial amount of time. Thus, the output capabilities of each operator are correspondingly limited. In addition, it will be appreciated that the mounting operation requires a skilled operator, further adding to the cost of fabrication of the lens.